Study on microstructure and permeability of a red clay area subjected to dry-wet cycles using X-ray micro computed tomography and AVIZO

Abstract

Global warming has significantly intensified the severity and frequency of dry-wet (DW) cycles, particularly in fragile ecological regions such as the Qinghai-Tibet Plateau, profoundly impacting soil structure and permeability. However, the report on the micro-scale pore structure and permeability of red clay in the Qinghai-Tibet Plateau is rare. In response, this study employs an innovative experimental technique to replicate the DW cycle of soil, combining with the micro-CT technology and permeability simulations, to evaluate the impact of DW cycles on the microstructure and permeability of red clay. The findings reveal that following a rising count of DW cycles, connected pore volume within the soil sample rapidly expands, while isolated pore volume initially decreases and then remains constant, highlighting the alterations in pore structure during the DW cycles. Following a rising count of DW cycles, connected porosity rises from 4.86 % to 16.06 %. This suggests that the increase in DW cycles results in the collapse of small pores and their merging into large pores. Permeability increases from 19.72 × 10⁻⁶ D to 250.76 × 10⁻⁶ D, exhibiting a trend of rapid growth followed by slow growth. Both the quantity and distribution density of visible flow lines progressively increase as the DW cycle number increases.